A. Introduction
In-mold coating (IMC) generally involves the production of a coated molded article by means of a process in which a coating film is inserted into a mold and then a resin is injected into the mold to perform injection molding, thereby transferring the coating resin of a transfer layer provided in the coating film onto a surface of the molded article.
In-mold decorating (IMD) generally involves the production of decorated molded article by means of a process in which a decorative film is inserted into a mold and then a resin is injected into the mold to perform injection molding, thereby decoratively transferring the pattern of a transfer layer provided in the decorative film onto a surface of the molded article.
While injection molding is the most commonly used IMC and IMD fabrication process, alternative processes [such as compression molding, spin casting, rotational molding, thermoforming, roll lamination, use of a platen/laminate press, blow molding, resin transfer molding (RTM), or reaction injection molding (RIM)] are also sometimes used. Injection molding is suitable for processing thermoplastic resins during IMC and IMD operations, while RIM enables the use of injection molding in IMC and IMD processes that require the molding of thermoset polymers.
Most IMD methods are transfer methods where an image is printed on a carrier film and then “transferred” to a molded article during the molding process. Some IMD methods use a carrier film with a durable coating resin that is printed and both the coating and decoration are transferred to the molded article during molding to produce a more durable decoration. (For brevity, in this disclosure, whenever the term “carrier film” is used, it will be understood to encompass both “carrier film” and “carrier sheet”.)
The following two subsections review representative examples from the IMC and IMD patent literature. The discussion of this patent literature, which is intended to help teach the invention disclosed in the present filing by providing a context to it, is not meant to imply that these patents necessarily constitute prior art. In fact, it will be seen that most of the patent literature on IMC and IMD processes focuses on the the use of IMC and IMD to incorporate thermoplastic polymer layers, with emphasis on the melt processing of thermoplastics and the design of molds for use in thermoplastic IMC and IMD processes and little or no applicability to thermoset IMC and IMD processes. By contrast, it will be seen also that the patent literature pertaining more specifically to thermoset IMC and IMD processes is rather limited.
The last subsection summarizes some of the limitations of existing IMC and IMD technologies using the RIM process to incorporate a thermoset layer for enhanced durability.
B. Coating Compositions and Processes
U.S. Pat. No. 2,245,651 discloses improved carbon film coatings for molds, and a new method for applying or depositing such films from a smoky flame of acetylene or other hydrocarbon materials for the protective coating of a mold surface in contact with a cast material.
U.S. Pat. No. 5,084,353 discloses that a fiberglass-reinforced plastic can be in-mold coated utilizing a free radical peroxide initiated thermosetting composition of at least one polymerizable epoxy-based oligomer having at least two acrylate groups, at least one copolymerizable ethylenically unsaturated monomer, at least one copolymerizable monoethylenically unsaturated compound having a —CO— group and an —NH2, —NH— and/or —OH group, and other conventional components such as at least one zinc salt of a fatty acid, at least one accelerator, at least one filler, and the like. These thermosetting compositions utilize a very low or nil amount of an adhesion agent such as a poly(vinyl acetate) and are stated to achieve better flow and good coverage at reduced coating weights as compared with earlier technologies.
U.S. Pat. No. 5,736,090 discloses a method of in-mold coating using a coating composition including: (A) a vehicle component including (i) a urethane acrylate oligomer or a urethane methacrylate oligomer, which is a reaction product containing no substantial unreacted isocyanate groups, of (a) an organic polyisocyanate, (b) an organic polyol and (c) a hydroxyalkyl acrylate or a hydroxyalkyl methacrylate, and (ii) a polymerizable unsaturated monomer, (B) a polyisocyanate compound, and (C) a polymerization initiator.
Japanese Patent No. JPS6337909 discloses a composition, which is prepared by mixing, for example, pentaerythritol triacrylate, triethylene oxide diacrylate, benzoyl peroxide and silicon-based leveling agent, is applied with a spray gun onto the cavity part, which allows to mold a plate-shaped molded item and is heated at a temperature of 90° C., of an injection mold and left under the state that the air in the cavity part of the mold is displaced with nitrogen gas. The resultant coating is hardened under the state mentioned above. Next, polycarbonate melted at 290° C. is injected in the mold and a molded item is removed from the mold after cooling. The outcome is that a hard and glossy thermoset acrylate film coating possessing good weather resistance is fully and integrally formed onto the outer surface of the polycarbonate molded item.
U.S. Pat. No. 6,235,228 discloses a method for on-mold (a technique that differs slightly from in-mold, as explained therein) surface coating fiberglass-reinforced molded articles during their manufacture with environmentally friendly and physiologically safe thermosetting unsaturated polyester on-mold coating powders which serve as replacements for liquid gel coats. The coating powders employed are adapted to cure at low temperatures to avoid causing thermal damage to the heat sensitive plastic molds which must be reused over and over again, and to cure in the presence of atmospheric oxygen to enable overcoating with liquid fill resins and fiberglass, which constitute the bulk of the finished article, without having the fill resins bleed through the powder coating film and detrimentally affect the overall quality of the surface finish.
U.S. Patent Application No. 2006078745 discloses composite plastic moldings containing A) a thermoplastically formable, heat-resistant composite film having A1) a carrier film of a thermoplastic resin and A2) a layer of a heat-resistant soft touch coating on one side of the carrier film (A1) and B) a thermoplastic layer on the side of the carrier film (A1) facing away from the soft touch coating, wherein the soft touch coating (A2) is obtained from a composition containing i) polyurethanes and/or poly(urethane urea)s which are free from hydroxyl and/or amine groups, ii) ionically modified polyurethanes and/or poly(urethane urea)s which contain hydroxyl and/or amine groups, iii) at least one crosslinking agent, iv) optionally film-forming resins other than A1) or A2), and v) optionally additives. It also discloses a process for the production of these composite moldings and their use in telecommunications equipment and in vehicle, ship and aircraft construction.
U.S. Patent Application No. 2010167045 discloses a reactive mixture for coating moldings via RIM, comprising at least 40% by weight of (meth)acrylates having at least two double bonds, the reactive mixture comprising at least one photoinitiator and at least one thermal initiator. It also describes a coated molding comprising a molding which is obtainable by injection molding processes and comprises at least one polymer selected from the group consisting of poly(methyl methacrylate), polymethylmethacrylimide, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer and poly(methyl methacrylate) copolymers, and a coating which is obtainable by polymerization of (meth)acrylates having at least two double bonds, the coating having an adhesive strength rating of not more than 1 according to the cross-hatch test and a decrease in gloss at 20° C. after a scratch resistance test according to ASTM D1044 (12/05) (applied weight 500 g, number of cycles=100) of not more than 10%. [ASTM D1044-13, “Standard Test Method for Resistance of Transparent Plastics to Surface Abrasion” (2013), which is the current version of this testing standard as of the date of this disclosure, is incorporated herein in its entirety by reference.] The reactive mixture is first thermally cured and, after the thermal curing, cured by irradiation, in a disclosed process for the production of coated moldings. It is shown, by comparing physical examples prepared according to the invention with comparative examples where curing was terminated after thermal cure so that the photocuring step was omitted, that the photocuring step is crucial for obtaining coatings manifesting high scratch resistance.
C. Decorating Compositions and Processes
U.S. Pat. No. 3,379,592 discloses a process for decorating a thermoset article such as dinnerware produced from a melamine-formaldehyde or urea-melamine-formaldehyde resin. This process involves the use, as the decorating medium, of a thermosetting resin ink in which the resin is partially pre-cured prior to the application of the decoration to the surface of the article. The curing process is completed after the application of the decoration.
U.S. Pat. No. 5,498,307 discloses methods for molding parts and for embedding a decorative, instructional or identifying pattern into the surface of molded products during a molding process. In some embodiments of this method, the pattern is formed as a pattern structure which is then applied to the inner surface of a mold. In a rotomolding process according this invention, the mold is charged with casting resin, heated and rotated. The pattern structure is molded into and becomes an integral part of the product.
Japanese Patent No. JPH1060127 discloses that a polyolefin resin (e.g. polypropylene) in an amount of 100 parts by weight is mixed with 5 to 1000 parts by weight of styrenic thermoplastic elastomer (such as a styrene/ethylene/butylene/styrene elastomer), and that the obtained mixture is processed by extrusion, calendering, non-stretched film molding, stretched film molding or the like to obtain a film 1. This film 1 is free from drawbacks inherent in vinyl chloride films, such as blushing and migration of a plasticizer, and can be used as an alternative for the vinyl chloride film. The formation of a pattern layer on the film 1 through a release layer optionally followed by formation of an adhesive layer thereon can provide a decorative sheet possessing excellent design effect, hand, and other properties.
U.S. Pat. No. 6,117,384 discloses an improved process for the manufacture of plastic articles such as automotive light assemblies, and the articles made by this process. The process includes a step wherein one or more colors are decorated onto a single film which is then incorporated with other components in an IMD process to yield the improved articles of the invention. For example, when using this method to manufacture a multi-colored taillight, it is usually preferable to have four discrete layers: (1) a polycarbonate film layer or other transparent substrate, to which a poly(vinylidene fluoride) (PVDF) film is laminated; (2) optionally, a layer of PVDF film or other material resistant to ultraviolet (UV) light; (3) a decorated layer printed on the exposed surface of the polycarbonate layer; and (4) a polycarbonate or other suitable substrate injection molded directly against the decorated layer.
U.S. Pat. No. 6,245,182 discloses a transfer material and surface protecting sheet which can provide a molded article excellent in abrasion resistance and chemical resistance without causing crack in curved part of the molded article. A transfer material or a surface protecting sheet of this invention has a substrate sheet, a protecting printed layer which consists of an active energy ray curable resin composition comprising a polyaddition reaction product having a urethane bond amount of from 6000 to 50000 g/eq as an effective ingredient on a surface of the substrate sheet, and an additional printed layer on the protecting printed layer or on the opposite surface of the substrate sheet.
U.S. Pat. No. 6,623,677 discloses a process for making a decorated article. The process entails printing, using a high temperature ink, a design on a surface of transfer paper, and transferring the design by sublimation to the surface of a clear flat substrate to obtain a decorated substrate. The thus decorated surface is then placed in a mold and thermoplastic resin is injected to form an article. The placing of the decorated substrate in the mold is such that the surface carrying the design faces the inside of the mold. An additional embodiment entails forming the decorated substrate to attain a three-dimensional decorated substrate prior to placing it in the mold. In a specific example, a polycarbonate based composition was used as the injected material and a polycarbonate film was used as the substrate. In another specific example, the substrate was a two-ply laminate of polycarbonate and PVDF.
U.S. Pat. No. 6,652,983 discloses a method for thermoplastic IMD whereby a decorating sheet is set in an injection mold and, after clamping the mold, molten molding resin is injected into the mold and allowed to cool and solidify. A portion of the in-mold decorating sheet becomes integrally bonded to a surface of the molding resin so that a decorated molded resin product is obtained. The decorative sheet has strong adhesion to the surface of the molded resin product over the area where they are integrally bonded, while being sufficiently brittle to enable the easy trimming of any unnecessary portion (any portion which had not become integrally bonded to the surface of the molding resin) from the surface of the molded resin product.
U.S. Pat. No. 7,927,711 discloses a durable layer for in-mold decoration. The durable layer is formed from a composition comprising (i) a thermally crosslinkable and photochemically or radically graftable polymer, (ii) a non-ethylenical thermal crosslinker, and (iii) a radiation curable multifunctional monomer or oligomer. It is stated that the durable layer has excellent surface quality with a wider geometric tolerance and can be formed at low cost.
U.S. Pat. No. 8,968,618 discloses a method of making a molded article having a curved surface, such as plates or serving trays, and the resulting molded articles. The in-mold label is a laminated film that includes a backing layer, a printed surface incorporating one or more designs thereon, a protective film layer, and one or more notches each having adjacent edges separated by a gap of predetermined distance and configured to intersect to ensure conformance of the in-mold label to the angled or curved peripheral portion of the article.
World Patent Application No. WO2004101293 discloses a method of preparing a molded article via IMD. The method includes providing a laminate of a plurality of separate realizable thermoplastic labels superimposed over a carrier film. A decoration is applied in-line to the exposed second surface of the labels, thereby forming a decorated laminate. The decorated laminate is forwarded and indexed into a mold such that the exposed first surface of the carrier film abuts at least a portion of the interior surface of the mold, and the decorated second surface of the label faces the interior space of the mold. A thermoplastic polymer is injected into the mold against the decorated surface of the label, forming a molded article. (Alternatively, RIM can be used to inject the reactive precursors of a thermosetting material such as polyurethane into the mold to form a thermoset molded article.) The carrier film is then separated from the molded article. At least a portion of the surface of the molded article prepared in accordance with the present method is defined by the first surface of at least one label. Molded articles that may be prepared according to this method include identification cards, such as driver's licenses and animal tags (e.g., cattle tags), and lenses, such as tinted ophthalmic lenses and sunshade lenses.
U.S. Patent Application No. 20070184148 exemplifies patents disclosing novel mold constructions to improve the efficiency of thermoplastic IMD processes and to thus achieve lower manufacturing costs and shorter delivery periods. By contrast, mold construction does not appear to have received much attention for thermoset IMD processes.
Japanese Patent No. JP2008049545 discloses a process providing a sheet for decoration which is used when a decorative molding having a fine uneven pattern is produced and can surely form unevenness as designed without deforming or eliminating the fine unevenness not only when the sheet itself is produced but when the sheet is heated or pressurized in the production of the decorative molding, or when the fine uneven pattern is formed in a product in the shape of deep drawing. In this process, in the heat-moldable sheet for simultaneous molding and decoration in which a decorative layer is formed on one side of a base material sheet, the surface on the opposite side of the decorative layer forming surface of the base material sheet is embossed, and the unevenness of the embossed surface is filled with a water soluble resin layer. The water-soluble resin layer is washed away after the removal of the decorated fabricated article from the mold, and the article shows both the decoration and the finely uneven embossed pattern.
U.S. Patent Application No. 20080152855 discloses a composition suitable for the formation of a release layer between the durable layer and the carrier layer in an IMD or thermal transfer printing process, and a process for the formation of a release layer comprising dispersing or dissolving the release layer composition in a solvent followed by curing this composition.
Japanese Patent No. JP2009166287 provides a decorative sheet for a simultaneous molding/decoration apparatus which prevents the use of a pattern having a defect so as to improve the yield of a decorative molding process. This process involves the use of inspection equipment containing a sensor that measures the transmission and reflection of light and thus identifies defects in the transfer layer optically. It then marks the defective portions of the transfer sheet. The use of defective portions of the transfer sheet during simultaneous molding/decoration can thus be avoided by skipping these portions containing defective patterns.
U.S. Patent Application No. 2010196651 discloses an object having a functional element embedded in its top surface and processes for its manufacturing. The object is in general formed by molding, stamping, lamination or a combination thereof. The functional element includes any electrical or mechanical elements that are capable of performing a function.
U.S. Patent Application No. 2010291329 discloses an in-mold label comprising a polymeric or cellulosic carrier base film (1) having a first decorative surface (1a) and a second, backing surface (1b), said label comprising a pattern (3) printed on said first decorative surface (1a) thereof, said printed first surface (1a) being laminated with a transparent protective top film (2), affixed thereto by means of an adhesive (4), the printed pattern (3) being visible through said transparent protective top film (2). It also discloses a method for manufacturing such a label and a method for incorporating it onto the surface of a polymeric article.
World Patent Application No. WO2012065966 discloses a process for overlaying a base substance with a multilayer decorative film in a thermoforming process, preferably in a vacuum forming process, wherein the process comprises the steps of (i) providing a multilayer decorative film comprising a hard coat layer (A), an adhesive layer (D), a base film layer (B) and optionally a design layer (C) between these layers (A) and (D), wherein the adhesive layer (D) comprises at least one latent reactive adhesive, (ii) applying the adhesive layer (D) of the decorative film to the surface of a base substance, and (iii) overlaying the base substance with the decorative film by heating at 70° C. or more. The resulting multilayer decorative films are claimed to have a degree of elongation of 10 to 1000% (preferably 50 to 1000%), a tensile strength of 50 to 1000 kg/cm2, a processing temperature of 70 to 220° C. (preferably 70 to 200° C.), adhesiveness of 50 N/25 mm or more, and durability of 1 week or more at 80° C. and 98% relative humidity.
Chinese Patent No. CN102673293 discloses thermal transfer IMD and a preparation method thereof that enable the high-resolution (600 dots per inch) printing of a PET film sheet, with the possibility of printing continuous patterns and gradient patterns, and color printing with high transparency and high transmittance on the PET back surface. Color saturation is high. The adhesion of a graphic ink layer and a PET film is strong. The decoration can survive high temperatures, can extend while the PET film is extended in a 3D thermal forming process, and has high extension. The extended surface is completed; the ink layer cannot be broken and has no wrinkles. The method not only can realize large-scale continuous production, but it can also overcome the shortcoming that hot-melt resin of the ink coating layer cannot survive high temperatures during the molding process. Products obtained by using the method cannot flush ink and glue and have complete patterns. These patterns manifest high gloss, anti-friction, anti-scratch, and weather resistance, so that they are durable. For example, biaxially oriented PET (BOPET) film was used as the carrier film, an adhesive was formulated, inks of various colors were used to create a pattern, and thermal transfer and injection molding were performed to transfer the pattern onto a PET substrate and to thus obtain a high-resolution printed PET film.
Chinese Patent No. CN102744939 discloses a thermoset IMD film and a preparation method thereof. The IMD film comprises a PET base film whose upper surface is provided with a scratch-resistant thermoset coating layer. An ink adhesion layer is provided on the lower surface of the PET base film. Adhesion of the ink layer on the film layer is provided. The preparation method comprises the steps of performing corona treatment on the PET base film; coating the PET base film; drying the coated PET base film; thermally curing the dried coated PET base film; coating the ink adhesion layer on the back of the cured dried coated PET base film; curing the PET film of which the back is coated with the ink adhesion layer; and rolling and cutting the film. The coating is strengthened by raising the temperature gradually to complete its crosslinking. The resulting thermoset IMD film has high transmittance, flexibility, and adhesion.
World Patent Application No. WO2014025005 discloses a multilayer film which has excellent surface hardness, excellent transparency, small thermal shrinkage, and high brittleness; and which (because it is sufficiently brittle) can be easily trimmed after decorative molding. The multilayer film comprises layer (A) containing a polycarbonate resin having a viscosity average molecular weight in the range of 13,000 to 20,000; and layers (B-1) and (B-2) that are laminated on both surfaces of the layer (A) and contain an acrylic resin. The entire thickness of the multilayer film is 50-200 microns. The thickness of layer (A) is 5-30% of the entire thickness.
U.S. Patent Application No. 2012315447 discloses a label for in-mold molding, which comprises a laminate film comprising a substrate layer (A) and a heat-sealable resin layer (B), wherein the substrate layer (A) comprises a thermoplastic resin in an amount of from 40 to 90% by weight and at least one of an inorganic fine powder and an organic filler in an amount of from 10 to 60% by weight, and the heat-sealable resin layer (B) comprises a thermoplastic resin in an amount of from 50 to 100% by weight.
U.S. Patent Application No. 2014113115 discloses a transfer film for in-mold molding which is stated to be superior in solvent resistance, heat resistance, durability, blocking resistance, and moldability, and is also stated to be capable of suppressing the generation of gate flow; and also provided is a method for producing such a film. The IMD layer of this film is constituted by a mixture composition containing at least one active-energy curable resin and at least one thermosetting resin.
D. Limitations of Existing IMC and IMD Technologies Using RIM
Existing thermoset IMC and IMD technologies that use RIM have several limitations:
(1) A method of decorating with printed images does not currently exist for the RIM process, and, in fact, for any other reactive molding process either. Since IMD is performed by using thermoplastic resins that are transferred to the molded article, this is not a viable method for RIM which uses reactive precursors that cure via exothermic reactions into thermoset resins. IMD for RIM is currently more of an in-mold painting system as it is limited to two-part polyurethane paint that covers over the entire article.
(2) If IMD were possible with RIM, it would be subject to the same issues, such as washout, as seen in IMD for thermoplastic molding methods. Washout is a distorted image due to resin flow and improper ink application and/or formulation.
(3) The white layer presents another potential issue. The resin color of a molded article affects the color of the ink layer. In general, the decoration will be more visible and vibrant if the resin color is lighter. For thermoplastic IMD, white can be printed under the other colors as the ink formulation allows the image to be transferred or bonded to the molded article. The exothermic reaction occurring during the RIM process will not allow a printed image or white layer as only a two-part gel coat which is not compatible with any printable system can be used with existing thermoset IMC and IMD technologies using RIM.
(4) Many IMD systems incorporate a multilayer system where a PET liner carries a printed polycarbonate sheet. The entire sheet bonds to the molded article during the molding process. Then the PET liner separates or releases from the polycarbonate sheet. This is not possible with the RIM process.
(5) While much work has been done to design optimum molds for thermoplastic IMC and IMD, little work has been done to design optimum molds for thermoset IMC and IMD via RIM.
It can be seen from the discussion above that a new combined IMC and IMD technology which alleviates some of these limitations of current thermoset IMC and IMD technologies that use RIM would be a significant development with many potential applications.